The matching operator _:::: compares _e_x_p_r_1 with _e_x_p_r_2, which must be a
regular expression. Regular expression syntax is defined is defined
in the _rrrr_eeee_gggg_cccc_oooo_mmmm_pppp_((((_5555_)))) man page under the section titled: _B_a_s_i_c _R_e_g_u_l_a_r
_E_x_p_r_e_s_s_i_o_n, Normally, the matching operator returns the number of
bytes matched (_0000 on failure). Alternatively, if the pattern
contains at least one regular expression subexpression [\( . . .\)],
the string corresponding to \1 will be returned.
The use of string arguments _llll_eeee_nnnn_gggg_tttt_hhhh, _ssss_uuuu_bbbb_ssss_tttt_rrrr, _iiii_nnnn_dddd_eeee_xxxx or _mmmm_aaaa_tttt_cccc_hhhh produces
The following example emulates _bbbb_aaaa_ssss_eeee_nnnn_aaaa_mmmm_eeee(1)-it returns the last segment of
the path name _$$$$_aaaa. For _$$$$_aaaa equal to either _////_uuuu_ssss_rrrr_////_aaaa_bbbb_cccc_////_ffff_iiii_llll_eeee or just _ffff_iiii_llll_eeee, the
example returns _ffff_iiii_llll_eeee. (Watch out for _//// alone as an argument: _eeee_xxxx_pppp_rrrr takes
it as the division operator; see the NOTES below.)